Increased speed and increased capacity of information transmission in recent years have led to widespread use of information communication using optical fibers. The information communication using optical fibers requires connection between optical fibers themselves or between an optical fiber and optical information equipment. Optical connectors such as ferrules for optical communication and fiber arrays for optical communication have been used for such connection. Demands for size reduction and high-density integration have led to a tendency toward the use of multi-core optical connectors.
Due to the nature of the structure of the optical connector that optical fibers are fitted into and fixed to respective insertion holes formed in a substrate, in order to prevent connection loss of optical fibers, the dimensional accuracy of insertion holes should be regulated on a submicron order from the viewpoint of avoiding deviation of the optical axis of the optical fibers. The adoption of the multi-core or reduced-size optical connector has led to a demand for higher dimensional accuracy.
In the case of conventional fiber arrays or ferrules manufactured by conducting injection molding or extrusion and then subjecting the molding to steps of baking and working, achieving the dimensional accuracy of insertion holes, into which optical fibers are to be inserted, within 1 μm is difficult due to the nature of the process.
To overcome this difficulty, for example, Japanese Patent Laid-Open No. 174274/1999 describes a structure in which V-shaped grooves are formed in a substrate such as a silicon dioxide or silicon substrate and optical fibers are held and fixed by a press cover. In this working method, unlike the above molding technique, V-shaped grooves are formed on a substrate by cutting, and finish processing is performed with a grind stone. In this method, the V-shaped grooves can be formed with dimensional accuracy within 0.5 μm.
This method, however, is disadvantageous in that the shape of the grind stone should always be corrected in order to keep the dimensional accuracy of V-shaped grooves on a constant level, resulting in poor productivity. Further, a press cover is necessary for holding optical fibers, and, in the case where V-shaped grooves are provided in a multiple array form, this press cover should be laid for each array. This imposes limitation on a size reduction and integration of the array for optical communication. Further, the conventional V-shaped grooves are disadvantageous in that, when optical fibers are inserted into the V-shaped grooves followed by pressing and fixation with the press plate, the gap between the substrate and the optical fibers is so large that the necessary amount of an adhesive used is large and, consequently, stress is applied to the optical fibers at the time of solidification of the adhesive, leading to deteriorated light transmission characteristics.
Accordingly, an object of the present invention is to provide a multi-cored fiber array for optical communication, which has high dimensional accuracy, can easily be prepared by machining, and is low in cost, and to provide a fiber array for optical communication which can reduce the necessary amount of an adhesive used for fixing optical fibers to the substrate.